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Journal of Cardiopulmonary Rehabilitation & Prevention

April 2011, Volume 31 Number 2 , p 111 - 119


  • Jonathan Singer MD, MS
  • Edward H. Yelin PhD
  • Patricia P. Katz PhD
  • Gabriela Sanchez BA
  • Carlos Iribarren MD, MPH, PhD
  • Mark D. Eisner MD, MPH
  • Paul D. Blanc MD, MSPH


Poor exercise capacity is a major complaint among persons with chronic obstructive pulmonary disease (COPD).1 Furthermore, as exercise capacity worsens, patients are more likely to curtail their normal activities and, thus, become disabled, consistent with classic models of disablement. Prevention of disability by clinicians, however, is hampered by a poor understanding of the specific causes of exercise limitation in COPD.2,3 Although lung function is the central physiologic impairment in COPD, spirometry data correlate poorly with the exercise capacity.4 Medical therapies have been developed that improve lung function and respiratory symptoms, but, in isolation, they do not improve exercise capacity reliably.5,6 To better prevent physical decline and disablement in COPD, the risk factors for exercise impairment must be elucidated clearly.Muscle dysfunction of the lower extremities has been identified as a specific cause of exercise impairment in COPD.7 Indeed, clinicians have long observed that patients with COPD cite leg fatigue as a key exercise-limiting factor. Consistent with this primal role, formal exercise testing is frequently terminated because of patient reports of generalized or leg-specific fatigue, rather than dyspnea.1 Moreover, recent evidence indicates that COPD is a systemic disease that may affect muscle function in patients with this condition.2,8 Most studies of muscle function in COPD, however, have been conducted only among patients with moderate-to-severe disease in highly selected clinical samples.3,9,10 It remains unknown whether decreased peripheral muscle strength is associated with decreased exercise capacity across a broad spectrum of COPD severity. Clarifying who is at risk is a prerequisite to the development and targeting of interventions to prevent functional decline. To determine whether decreased leg and respiratory muscle strength are associated with exercise limitation and decreased lower extremity functioning in subjects over

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